Gatling how to store and load a value for a later request - gatling

Question

I'd like to build a load test where the second request is fed from first response. The data extraction is done in a method because it is not only one line of code. My problem is storing the value (id) and load it later. How should the value be stored and loaded? I tried some different approaches, and I come up with this code. The documentation has not helped me.
object First {
val first = {
exec(http("first request")
.post("/graphql")
.headers(headers_0)
.body(RawFileBody("computerdatabase/recordedsimulation/first.json"))
.check(bodyString.saveAs("bodyResponse"))
)
.exec {
session =>
val response = session("bodyResponse").as[String]
session.set("Id", getRandomValueForKey("id", response))
session}
.pause(1)
}
}
object Second {
val second = {
exec(http("Second ${Id}")
.post("/graphql")
.headers(headers_0)
.body(RawFileBody("computerdatabase/recordedsimulation/second.json"))
)
.pause(1)
}
}
val user = scenario("User")
.exec(
First.first,
Second.second
)
setUp(user.inject(
atOnceUsers(1),
)).protocols(httpProtocol)

Answer 1

Your issue is that you're not using the Session properly.
From the documentation:
Warning
Session instances are immutable!
Why is that so? Because Sessions are messages that are dealt with in a multi-threaded concurrent way, so immutability is the best way to deal with state without relying on synchronization and blocking.
A very common pitfall is to forget that set and setAll actually return new instances.
This is exactly what you're doing:
exec { session =>
val response = session("bodyResponse").as[String]
session.set("Id", getRandomValueForKey("id", response))
session
}
It should be:
exec { session =>
val response = session("bodyResponse").as[String]
session.set("Id", getRandomValueForKey("id", response))
}